A number of neurological diseases are characterized by neurodegeneration. For example, Parkinson's disease (PD) is a debilitating neurological disorder marked by tremor, bradykinesia, rigidity and poor balance. PD is associated with the loss of dopaminergic neurons in the brain, particularly in the substantia nigra. Other disease state characterized by neurodegeneration include, but are not limited to, Alexander disease, Alper's disease, Alzheimer's disease, amyotrophic lateral sclerosis, ataxia telangiectasia, Batten disease, bovine spongiform encephalopathy (BSE), Canavan disease, Cockayne syndrome, corticobasal degeneration, Creutzfeldt-Jakob disease, Huntington disease, HIV-associated dementia, Kennedy's disease, Krabbe disease, Lewy body dementia, Machado-Joseph disease (Spinocerebellar ataxia type 3), multiple sclerosis, multiple system atrophy, narcolepsy, neuroborreliosis, Pelizaeus-Merzbacher disease, Pick's disease, primary lateral sclerosis, Refsum's disease, Sandhoff disease and Schilder's disease.
14-3-3 proteins are a family of highly conserved acidic 30-kd proteins found throughout the evolutionary scale, from yeasts to human. There are seven 14-3-3 isoforms in mammals named β, γ, ε, ζ, η, θ (also termed as τ), and σ (Dougherty and Morrison, J Cell Sci, 117:1875-84, 2004). Although the 14-3-3 protein is widely distributed in neural and non-neural tissues, it is expressed most abundantly in neurons in the central nervous system (CNS) where it can represent more than 1% of total protein.
These proteins contain five highly conserved regions that are separated by less homologous regions (Gardino, et al. Semin Cancer Biol 16, 173-82, 2006). The conserved regions are involved in ligand binding and dimerization (Berg, et al., Nat Rev Neurosci 4, 752-62, 2003). The unconserved carboxyl termini probably regulate 14-3-3 function and stabilize the unbound form. Phylogenetic analysis of the different isoforms suggest three subgroups among the isoform: 1) γ and η 2) β, θ, ε and ζ and 3) σ.
These proteins form homo- or heterodimers that lack intrinsic enzymatic activity. As dimers, 14-3-3s form a highly conserved concave amphipathic groove that mediates interactions with ligand. The amphipathic groove is a large cup-like structure with two ligand-binding sites in its groove. The dimeric complex acts as a novel molecular chaperone that interacts with key molecules involved in cell differentiation, proliferation, transformation, and apoptosis (van Hemert M J et al., Bioessays; Aitken A, et al., Biochem Soc Trans. 2002; 30:351-360; Berg D, et al., Nature Rev Neurosci. 2002; 4:752-762). 14-3-3 protein regulates the function of target proteins by restricting their subcellular location, bridging them to modulate catalytic activity, and protecting them from dephosphorylation or proteolysis (Muslin A J, et al., Cell Signal. 2000; 12:703-709; Yaffe M B, FEBS Lett. 2002; 513:53-57; Tzivion G, et al., J Biol. Chem. 2002; 277:3061-3064).
In general, the 14-3-3 protein binds to phosphoserine-containing motifs of the ligands such as RSXpSXP (SEQ ID NO. 7) and RXY/FXpSXP (SEQ ID NO. 8) in a sequence-specific manner (where X is any amino acid and p represents a phosphorylated residue). More than 300 proteins have been identified as being 14-3-3 binding partners. These binding partners participate in a wide range of cellular functions, including primary metabolism, cell proliferation, actin dynamics, proteosomal function, transcription, and apoptosis. In the central nervous system, proposed functional roles for 14-3-3s include neuronal migration during development, learning, and neurodegeneration. The binding partners include a range of intracellular signaling regulators such as Raf, BAD, protein kinase C (PKC), phophatidylinositol 3-kinase (PI3K), and cdc25 phosphatase. Binding of the 14-3-3 protein to Raf is indispensable for Raf kinase activity in the Ras/MAPK signaling pathway, whereas 14-3-3 binding to the mitochondrial Bcl-2 family member BAD, when phosphorylated by a serine/threonine kinase Akt, inhibits apoptosis. In addition to the phosphorylation-dependent interaction, the 14-3-3 protein can interact with a set of target proteins in a phosphorylation-independent manner (Zhai et al., J Biol Chem. 2001; 276:41318-411324). The ε isoform binds to p190RhoGEF via a phosphoserine-independent interaction.
Previous studies indicated that the 14-3-3 protein has isoform-specific and nonredundant functions (Broadie K, et al., Neuron. 1997; 19:391-402). Synaptic transmission and associative learning are impaired in Drosophila mutants lacking the ζ protein. The 14-3-3 isoforms have distinct affinities for their target proteins. A preferential interaction is observed between PKCθ and the human 14-3-3θ isoform in T cells (Meller N, et al., Mol Cell Biol. 1996; 16:5782-5791), IGF1-receptor, IRS1, and ε isoform (Craparo A, et al., J Biol Chem. 1997; 272:11663-1), the apoptosis-inhibitor A20 and the human β and η isoforms (Vincenz C, et al., J Biol Chem. 1996; 271:20029-20034), and glucocorticoid receptor and the human η isoform (Wakui H, et al., J Biol Chem. 1997; 272:8153-8156). The human β and ζ isoforms and not γ or ε isoforms interact with phosphorylated tau (Hashiguchi M, et al., J Biol Chem. 2000; 275:25247-25254). Furthermore, different isoforms show distinct patterns of spatial, temporal, and subcellular distribution. In the developing rat brain, defined populations of neurons express β, γ, ζ, and θ isoforms at specific stages of development (Watanabe M, et al., Mol Brain Res. 1993; 17:135-146, Watanabe M, et al., Mol Brain Res. 1994; 25:113-121). In the adult mouse brain, β, γ, η, and ζ isoforms are widely distributed with the localization primarily in neurons, although some glial cells express ε, θ, and ζ isoforms (Baxter H C, et al., Neuroscience. 2002; 109:5-14).
Recently, several lines of evidence have indicated that the 14-3-3 protein is involved in neurodegenerative processes. The 14-3-3 protein detected in the cerebrospinal fluid of Creutzfeldt-Jacob disease has been used as a biochemical marker for the premortem diagnosis of Creutzfeldt-Jacob disease in the context of differential diagnosis of progressive dementia. However, recent studies showed that the 14-3-3 protein is occasionally detectable in the cerebrospinal fluid of infectious meningoencephalitis, metabolic encephalopathy, cerebrovascular diseases, and multiple sclerosis presenting with severe myelitis, suggesting that 14-3-3 protein is not a marker specific for prion diseases but for extensive destruction of brain tissues causing the leakage of 14-3-3 protein into the cerebrospinal fluid. In the Alzheimer's disease brain, neurofibrillary tangles express immunoreactivity against the 14-3-3 protein (Layfield R, et al., Neurosci Lett. 1996; 209:57-60). The 14-3-3ζ homodimer interacts with tau and glycogen synthase kinase-3β (GSK3β), and stimulates GSK3β-mediated tau phosphorylation.
In the Parkinson's disease brain and in Dementia with Lewy Bodies, Lewy bodies possess γ, ε, ζ, and θ isoforms that interact with α-synuclein (α-syn) (Berg D, et al., Ann Neurol. 2003; 54:135, Ostrerova N, et al., J Neurosci. 1999; 19:5782-5791). 14-3-3 proteins have been found in Lewy Bodies in multiple System Atrophy. Dopamine-dependent neurotoxicity is mediated by a soluble complex composed of the 14-3-3 protein and α-synuclein, whose levels are markedly elevated in the substantia nigra of the Parkinson's disease brain (Xu J, et al., Nat Med. 2002; 8:600-606). The neurotoxicity of ataxin-1, the causative protein of spinocerebellar ataxia type 1, is enhanced by ε and ζ isoforms that bind to and stabilize ataxin-1 phosphorylated by Akt, thereby slowing its degradation (Chen H-K, et al., Cell. 2003; 113:457-468). Finally, expression of the θ isoform is enhanced in the spinal cord of amyotrophic lateral sclerosis (Malaspina A, et al., J Neurochem. 2000; 75:2511-2520). However, it remains unknown whether the 14-3-3 protein plays an active role in the pathological process of MS.
14-3-3 proteins share considerable homology with α-syn (Ostreova, N, et al., J Neuroscu, 19:1578-91, 1999) and 14-3-3 proteins can be co-immunoprecipitated with α-syn from mammalian brains (Ostreova, N, et al., J Neuroscu, 19:1578-91, 1999; Xu, J, et al., Nat Med, 8:600-06, 2002). Increased co-immunoprecipitation is observed in the nigra of PD brains (Xu, J, et al., Nat Med, 8:600-06, 2002). In recent studies, the protein α-syn has been discovered to have a central role in the pathogenesis of PD. Families with mutant α-syn exhibit autosomal dominant PD (Athanassiadou, A, et al., Am J Hum Genet, 66:555-08, 1999; Kruger, R. et al., Nat Genet, 18:106-08, 1998; Polmeropoulos, M H, et al., Science, 276:2045-47, 1997; Zarranz, J J, et al., Ann Neurol, 55: 164-73, 2004). α-syn gene multiplication, causing an increase in the amount of normal α-syn present, is sufficient to trigger PC (Singleton, A B, et al., Science, 302:841, 2003). In addition α-syn aggregates are observed in sporadic PD (Spillantini, M G, et al., Nature, 388:839-40, 1997) and insoluble α-syn is increased in sporadic PD and the related condition Dementia with Lewy Bodies (DLB) (Cantuti-Castelverti, I, et al., J Neuropathol Exp Neurol, 64:1058-66, 2005). Furthermore, transgenic mice expressing mutant or wild-type α-syn show motor deficits, alterations in dopaminergic terminals and α-syn positive inclusions (Maries, E, et al., Nat Rev Neurosci, 4:727-38, 2003). Rats and primates virally injected with mutant or wild-type α-syn into the substantia nigra show nigral dopaminergic cell loss (Maries, E, et al., Nat Rev Neurosci, 4:727-38, 2003).
The art is currently in need of novel methods for the treatment and prevention of neurodegeneration and diseases associated with neurodegeneration. Although 14-3-3 proteins are implicated in neurodegeneration in a variety of models, the mechanisms by which 14-3-3 proteins contribute to such neurodegeneration are poorly understood. As a result, therapies for treatment and prevention of neurodegeneration are currently lacking. The present disclosure provides novel methods for the prevention and treatment of neurodegeneration and disease states characterized, at least in part, by neurodegeneration.